/Engine/Plugins/Media/MediaPlayerEditor/Source/MediaPlayerEditor/Public/Widgets/SMediaPlayerEditorViewer.h
The concession is to return a can_handled/cannot_handle boolean rather than a fullFReply.
A reply that indicated whether the contents of the DragDropEvent can potentially be processed by this widget.
virtual void OnDragEnter ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & MyGeometry, const [FDragDropEvent](API\Runtime\SlateCore\Input\FDragDropEvent) & DragDropEvent )